WEDNESDAY, Feb. 14, 2018 (HealthDay News) -- Just in time for Valentine's Day, new research suggests one behavior can predict how strong a couple's bond might be.

The study of newlywed couples found that if either partner spent too much time looking at attractive members of the opposite sex, their marriage was prone to trouble down the road.

A research team from Florida State University tracked marital outcomes for 233 couples for up to 3.5 years.

First, though, they presented husbands and wives with a little test. Each newlywed was shown photos of both highly attractive or only middling-attractive men and women.

Tracked over time, the study found that men and women who lingered on the photos for a longer time were more likely to be unfaithful than those who spent less time doing so.

Even a small time difference spent looking was significant. People who looked away from a photo of an attractive member of the opposite sex in as little as a few hundred milliseconds faster than average were nearly 50 percent less likely to be unfaithful to their spouse.

"People are not necessarily aware of what they're doing or why they're doing it," study author Jim McNulty said in a university news release. "These processes are largely spontaneous and effortless, and they may be somewhat shaped by biology and/or early childhood experiences."

The study participants were also asked to evaluate just how attractive the people depicted in the photos were. People who tended to "downgrade" the allure of those they saw in the photos were also less likely to cheat in a marriage, compared to those who described the people as very attractive.

Other strong predictors of infidelity included age, satisfaction with marriage, sexual satisfaction, attractiveness and history of short-term relationships.

Younger people and (not surprisingly) those less satisfied with their marriage were more likely to be unfaithful, as were men who had had more short-term sexual partners before they got hitched.

But there was perhaps one surprise: People who were satisfied with sex in their marriage were actually more likely to be unfaithful, McNulty's team said.

The researchers theorize that these people may feel more "positive" about sex in general so they'll seek it out elsewhere -- even if they feel satisfied within their marriage.

Attractiveness mattered, too. Less attractive women were more likely to have an affair compared to their more attractive female peers, the study found. And men with less attractive wives were more apt to stray versus guys married to more beautiful women.

The study was published Feb. 12 in the Journal of Personality and Social Psychology.

The researchers note that the divorce rate in the United States is 40 to 50 percent, with social media now making it easier than ever to connect with others. That means new ways may be needed to help people maintain long-term relationships.

"Understanding how people avoid the temptation posed by alternative partners may be more relevant than ever to understanding relationships," McNulty said.